1. Field of the Invention
The illustrative embodiments of the invention relate generally to a pump for fluid and, more specifically, to a pump having two cavities in which each pumping cavity is a substantially disc-shaped, cylindrical cavity having substantially circular end walls and a side wall and which operates via acoustic resonance of fluid within the cavity. More specifically, the illustrative embodiments of the invention relate to a pump in which the two pump cavities each have a different valve structure to provide different fluid dynamic capabilities.
2. Description of Related Art
It is known to use acoustic resonance to achieve fluid pumping from defined inlets and outlets. This can be achieved using a long cylindrical cavity with an acoustic driver at one end, which drives a longitudinal acoustic standing wave. In such a cylindrical cavity, the acoustic pressure wave has limited amplitude. Varying cross-section cavities, such as cone, horn-cone, and bulb shaped cavities have been used to achieve higher amplitude pressure oscillations, thereby significantly increasing the pumping effect. In such higher amplitude waves, non-linear mechanisms that result in energy dissipation are suppressed by careful cavity design. However, high amplitude acoustic resonance has not been employed within disc-shaped cavities in which radial pressure oscillations are excited until recently. International Patent Application No. PCT/GB2006/001487, published as WO 2006/111775 (the '487 Application), discloses a pump having a substantially disc-shaped cavity with a high aspect ratio, i.e., the ratio of the radius of the cavity to the height of the cavity.
The pump described in the '487 application is further developed in related patent applications PCT/GB2009/050245, PCT/GB2009/050613, PCT/GB2009/050614, PCT/GB2009/050615, and PCT/GB2011/050141. These applications and the '487 Application are included herein by reference.
It is important to note that the pump described in the '487 application and the related applications listed above operates on a different physical principle to the majority of pumps described in the prior art. In particular, many pumps known in the art are displacement pumps, i.e. pumps in which the volume of the pumping chamber is made smaller in order to compress and expel fluids through an outlet valve and is increased in size so as to draw fluid through an inlet valve. An example of such a pump is described in DE4422743 (“Gerlach”), and further examples of displacement pumps may be found in US2004000843, WO2005001287, DE19539020, and U.S. Pat. No. 6,203,291.
By contrast, the '487 application describes a pump that applies the principle of acoustic resonance to motivate fluid through a cavity of the pump. In the operation of such a pump, pressure oscillations within the pump cavity compress fluid within one part of the cavity while expanding fluid in another part of the cavity. In contrast to the more conventional displacement pump, an acoustic resonance pump does not change the volume of the pump cavity in order to achieve pumping operation. Instead, the acoustic resonance pump's design is adapted to efficiently create, maintain, and rectify the acoustic pressure oscillations within the cavity.
Turning now to the design and operation of an acoustic resonance pump in greater detail, the '487 Application describes a pump having a substantially cylindrical cavity. The cylindrical cavity comprises a side wall closed at each end by end walls, one or more of which is a driven end wall. The pump also comprises an actuator that causes an oscillatory motion of the driven end wall (i.e., displacement oscillations) in a direction substantially perpendicular to the end wall or substantially parallel to the longitudinal axis of the cylindrical cavity. These displacement oscillations may be referred to hereinafter as axial oscillations of the driven end wall. The axial oscillations of the driven end wall generate substantially proportional pressure oscillations of fluid within the cavity. The pressure oscillations create a radial pressure distribution approximating that of a Bessel function of the first kind as described in the '487 Application. Such oscillations are referred to hereinafter as radial oscillations of the fluid pressure within the cavity.
The pump of the '487 application has one or more valves for controlling the flow of fluid through the pump. The valves are capable of operating at high frequencies, as it is preferable to operate the pump at frequencies beyond the range of human hearing. Such a valve is described in International Patent Application No. PCT/GB2009/050614.
The driven end wall is mounted to the side wall of the pump at an interface, and the efficiency of the pump is generally dependent upon this interface. It is desirable to maintain the efficiency of such a pump by structuring the interface so that it does not decrease or dampen the motion of the driven end wall, thereby mitigating a reduction in the amplitude of the fluid pressure oscillations within the cavity. Patent application PCT/GB2009/050613 (the '613 Application, incorporated by reference herein) discloses a pump wherein an actuator forms a portion of the driven end wall, and an isolator functions as the interface between actuator and the side wall. The isolator provides an interface that reduces damping of the motion of the driven end wall. Illustrative embodiments of isolators are shown in the figures of the '613 Application.
The pump of the '613 Application comprises a pump body having a substantially cylindrical shape defining a cavity formed by a side wall closed at both ends by substantially circular end walls. At least one of the end walls is a driven end wall having a central portion and a peripheral portion adjacent the side wall. The cavity contains a fluid when in use. The pump further comprises an actuator operatively associated with the central portion of the driven end wall to cause an oscillatory motion of the driven end wall in a direction substantially perpendicular thereto. The pump further comprises an isolator operatively associated with the peripheral portion of the driven end wall to reduce dampening of the displacement oscillations caused by the end wall's connection to the side wall of the cavity. The pump further comprises a first aperture disposed at about the center of one of the end walls, and a second aperture disposed at another location in the pump body, whereby the displacement oscillations generate radial oscillations of fluid pressure within the cavity of the pump body causing fluid flow through the apertures.